Abstract

In shale reservoirs, the characteristic length of the physical system is close to the mean free path of the gas and conventional Darcy flow models fall apart. The dominant types of gas flow falls between the transition regime between Darcy flow and Knudsen flow. The intermediate flow regime is modeled as a combination of Knudsen flow and Darcy flow. In this paper, we show the contribution of Knudsen flow to total flow as we decrease the pore-size. The results of this modeling show that Knudsen flow increases sharply as pore sizes reduce to smaller than 100 nm. In shales, the relative abundance of these small pore sizes compared to large pore sizes control the flow regime.